The present invention relates to a method for making aromatic etherimides by effecting the condensation of a phenoxide salt with a nuclear-substituted phthalimide in the presence of a nonpolar solvent and a phase transfer catalyst. More particularly, the present invention relates to a method for making an aromatic ether phthalimide or an aromatic bis(ether phthalimide).
Prior to the present invention, methods involving the condensation of an alkali metal phenoxide with a nuclear substituted phthalimide as shown by Heath et al U.S. Pat. Nos. 3,879,428, 3,957,862 and 3,956,320, assigned to the same assignee as the present invention, or Meyers U.S. Pat. No. 3,965,125, were generally based on the use of a dipolar aprotic solvent to facilitate reaction. Those skilled in the art know that it is often economically unattractive to effect the synthesis of various organic materials using dipolar aprotic solvents because such solvents are expensive and often subject to a variety of chemical side reactions which render them useless for recycling.
An improved method for making aromatic etherimides is shown by Williams, U.S. Pat. No. 4,273,712, assigned to the same assignee as the present invention and incorporated herein by reference. The method of Williams is based on the use of a quaternary ammonium salt as a phase transfer catalyst which allows for the use of a nonpolar solvent in place ofthe dipolar aprotic solvents used in the prior art. Although the method of Williams provides for improved results with respect to the elimination of dipolar aprotic solvents, it has been found that the use of such quaternary ammonium phase transfer catalyst may result in the production of toxic nitrosamines which can interfere with the use of such quaternary ammonium salt catalyst as phase transfer catalysts in industrial methods for making aromatic etherimides.
The present invention is based on the discovery that an effective amount of a triorganoborate of the formula, ##STR1## where R, R.sup.1 and R.sup.2 are selected from monovalent C.sub.(1-13) hydrocarbons radicals and substituted C.sub.(1-13) hydrocarbon radicals and G is a divalent radical selected from oxygen and sulfur, can be used as phase transfer catalysts for making aromatic etherimides of the formula, ##STR2## In addition to avoiding the generation of nitrosamines, the use of the triorganoborates of formula (1) as phase transfer catalyst for aromatic etherimide formation does not require the use of a dipolar aprotic solvent. Reaction can be effected between an alkali metal phenoxide salt or diphenoxide salt, and a nuclear substituted phthalimide in a nonpolar organic solvent, where R.sup.3 is a monovalent radical selected from hydrogen, a C.sub.(1-8) alkyl radical and C.sub.(6-13) aryl radical, R.sup.4 is a C.sub.(6-30) aromatic organic radical, and a is an integer equal to 1 or 2, and when a is 1, R.sup.4 is monovalent and when a is 2, R.sup.4 is divalent.